vacuum concentration/distillation may work. essentially putting the liquid under a vacuum causes the liquid to boil without having to heat it as much/at all. A rotary evaporator would do it but costs 2,000-15,000. alternatively you could hook a sidearm flask to a vacuum pump on a stirring hot plate for much less but it would probably take longer. A spray dryer would work but similarly costs a lot, however you can replicate the process with inexpensive tools (essentially the theory is that a slurry such as your stevia liquid is sprayed to fine particles into a hot chamber (350F+) and dried by the heat). It's touchy because too little heat will do nothing and too much will burn the powder but I've seen it done with a paint sprayer and a heat gun in an enclosed container (e.g. a pipe or trashcan depending on scale)

I love instructables! The best machine would be a lab-sized (aka "benchtop" or "table top") rotary drum dryer, since the split second the liquid hits the stainless drum it solidifies, and is instantly scraped off. Buflovak makes them, but they are very expensive:

Here is an equally-effective approach, frequently used in labs to turn liquids into powders. Cellulose fiber is natural plant fiber to make stems erect and strong (think celery). Cellulose absorbs many times its weight in liquid, such as stevia liquid. A commercial form of cellulose called "SolkaFloc" absorbs many times its weight in liquid. You would soak the cellulose with Stevia liquid, then dehydrate it in the sun, or using a home dehydrator.

Image 2: Powdered Cellulose Fiber

Dehydrate the soaked cellulose at 125-135 degrees. The water should dehydrate rapidly due to the cellulose's high surface area. Drying options include a home oven, a mini clothes dryer, or a food dehydrator.

Image 3: Mini Clothes Dryer

Image 4: Home Food Dehydrator

When dry, grind it using a coffee grinder: the kind with burrs give the most uniform particle size, but you could use a rocket blender.

The difficult thing is usually getting the liquid to evaporate quickly enough to keep it from being olonized by microbes (fermenting at best, getting moldy at worst), and without cooking the material or driving off essential oils you want to preserve, either of which could change its flavor.

Have you considered just freezing your concentrate into ice cubes, perhaps using one of the plastic trays which makes 1/2 inch cubes? You could then just toss an appropriate number of cubes into whatever you're using. (Credit for this approach goes to Ewel Gibbons, who used it to preserve jewelweed extract for later use.)

As has been noted, making dry liquids is usually done using a vacuum process. Using conventional dehydration will evaporate all the aromatic oils from your Stevia, and it will potentially introduce harmful bacteria or simply result in spoil, so freezing in convenient measurements is probably the best you can hope for at home.

Do you have any expereance with such food driers? Can I use a food drier for liquids? A food drier dries the inside stuff, by making the stuff warm inside and the liquid comes out of the stuff? What about an oven with an open door? The heat above 50°C and under 100°C so that nothing burnes inside?